1. Field of the Invention
This invention relates generally to ultrasonic welding machines and, more specifically, to ultrasonic welding machines for forming tabs on pleats of woven and nonwoven fabric
2. Description of the Prior Art
It is generally known in the blind industry to fold blind fabric into pleats. It is further known that certain advantages may be obtained by providing a tab along pleats of the fabric. These advantages include improved pleat retention, that is the tab allows the fabric to retain its shape and prevents the fabric from losing its creases and going flat. Also, the cording holes and the cords themselves may be located through the tab and can thus be "hidden" from view. It is known to form this tab by ultrasonic welding.
Such tabbed pleats are described in U.S. Pat. No. 4,974,656 to Judkins. FIG. 9, which is a prior art figure derived from a figure of the Judkins patent, depicts such a tabbed pleated shade. Prior art FIG. 9, which includes reference numerals, shows a section of fabric creased so as to form a pleat that extends longitudinally along the section of fabric. A weld line 124 is placed along the length of the pleat at some distance from the creased edge of the fabric so as to form a tab 122 that lies longitudinally along the fabric, parallel with the pleat. Window blind lift cords 128 may then be placed through holes on the tab of the pleated shade. Although welding is the preferred manner of forming the pleat tabs, other means such as sewing or gluing are also common in the industry.
The methods used in the industry for forming tabs on pleats have included the use of machines having a long, toothed spindle. These spindles index the fabric forward pleat by pleat into position to be welded. It is also known in the industry to employ machines that have two or more thinner spindles rather than one long spindle to index the fabric when forming tabs.
A known method of forming a tab on the pleat is through the use of ultrasonic welding. In ultrasonic welding, the overlapping sections of material to be welded are placed upon an anvil. The anvil supports the material during welding.
Located above the material to be welded are the stacks. A stack consists of a converter, a booster and a horn in series, with the horn facing the material. The horn has the function of delivering the energy to the material to be welded. The stacks are lowered to apply a clamping force on the material between the horn and anvil, which results in the material between the horn and anvil being put under pressure. At some point while this welding pressure is mounting, the welding commences. A problem that is present in the art is structure deflection during the welding operation. If the anvil warps or deflects during the welding operation, the welding pressure will vary thus creating inconsistent and possibly defective welds. Similarly, the welding pressure may vary if the supports to which the stacks are mounted deflect.
Once welding is complete, the stack must be moved away from the material so that the welded pleat can be removed from the anvil and the next pleat indexed forward for welding. If the fabric is not positively situated on the anvils during welding, a missed weld or a weld not in its proper location on the blind fabric could result. Thus, an effective system for positively situating the fabric in position for welding is needed.
Typically, stacks are actuated mechanically and mechanical means such as springs are normally employed to insure proper welding pressure. However, if the springs are worn, incorrectly adjusted or otherwise provide too much or too little tension then too much or too little pressure is applied to the material during welding. Too little welding pressure results in bad welds, while excessive welding pressure can cause premature wear to the stack components. Thus, a means of individually regulating the welding pressure of a stack is needed. Another problem with spring loaded systems is that whenever there is a change in any physical characteristic of the fabric, the system may need to be adjusted.